Process control systems require the accurate measurement of process variables. Typically, a sensor in the form of a primary element senses the value of a process variable and a transmitter develops an output having a value that varies as a function of the process variable. For example, a level transmitter includes a primary element for sensing level and a circuit for developing an electrical signal representing sensed level.
Knowledge of level in industrial process tanks or vessels has long been required for safe and cost-effective operation of plants. Many technologies exist for making level measurements. These include buoyancy, capacitance, ultrasonic and microwave radar, to name a few.
In one form, a through air measurement instrument, such as a microwave radar level transmitter, launches a radar signal which reflects off a liquid or other surface and the instrument measures time of flight between transmission and reception of the radar signal. Electrical energy is converted to an electromagnetic wave from a launch element. The wave propagates through free space.
An electronic enclosure includes an RF circuit which may include the launch element on a printed circuit board. The launch element may be configured to use linear polarization or circular polarization. With circular polarization, the launching element creates radiation where the electric field rotates at increasing distances from the launching element. A magnetic wave is passed through a waveguide. The waveguide is specifically defined according to the operating frequency. With a high frequency signal such as in the K-3 band, which operates at about 26 GHz, the overall design of the waveguide is important and the waveguide must be enclosed at a near end to satisfy these requirements.
Moreover, with very high frequency radar signals it is necessary to avoid problems caused by RF signal leaking out and possible radiation loss from the launching element at the very high microwave frequencies. It is also necessary to reduce cross talk between adjacent traces forming the launching element.
The present invention is directed to solving one or more of the problems discussed above in a novel and simple manner.